The present invention relates to a silver halide photographic light-sensitive material and, more particularly, to a silver halide photographic light-sensitive material having a high sensitivity, a low fog, and a high storage stability.
Conventionally, a lot of efforts have been made to increase the sensitivity of silver halide photographic light-sensitive materials. It is known that sensitizing dyes used for spectral sensitization have a large influence on the performance of silver halide photographic light-sensitive materials. A slight structural difference between sensitizing dyes has a large effect on photographic properties such as sensitivity, fog, and storage stability. Since it is difficult to predict the effect in advance, a large number of researchers have conventionally made efforts to synthesize a number of sensitizing dyes and examine the photographic properties of these dyes.
Also, to raise the sensitivity of silver halide photographic light-sensitive materials, reduction sensitization has been attempted for a long time. For example, U.S. Pat. No. 2,487,850, U.S. Pat. No. 2,512,925, and British Patent 789,823 have disclosed that a tin compound, a polyamine compound, and a thiourea dioxide-based compound, respectively, are useful as reduction sensitizers. Furthermore, "Photographic Science and Engineering", Vol. 23, page 113 (1979) compares the properties of silver nuclei formed by various reduction sensitization methods and uses methods using dimethylamineborane, stannous chloride, hydrazine, high-pH ripening, and low-pAg ripening. Methods of reduction sensitization are also disclosed in U.S. Pat. Nos. 2,518,698, 3,201,254, 3,411,917, 3,779,777, and 3,930,867. Improvements of reduction sensitization methods, as well as selection of reduction sensitizers, are described in JP-B-57-33572 ("JP-B" means Published Examined Japanese Patent Application) and JP-B-58-1410.
Unfortunately, the research by the present inventors has revealed that when spectral sensitization is performed by causing reduction-sensitized silver halide grains to adsorb sensitizing dyes, especially when green and red regions are spectrally sensitized, it is very difficult to obtain a sufficient spectral sensitivity without bringing about an action (e.g., an increase in fog) undesirable to photographic properties.
A method by which a sensitizing dye in a light-sensitive material is adsorbed at a high temperature (50.degree. C. or higher) in order to prevent silver halide grains from adsorbing the sensitizing dye (especially when the humidity is high) or a method by which a sensitizing dye is adsorbed before chemical sensitization to increase the sensitivity is widely known. However, the fog is significantly raised when these methods are applied to a case where a reduction-sensitized emulsion is made to adsorb a spectral sensitizing dye in a green or red region.
For the reasons described above, a technique which spectrally sensitizes reduction-sensitized silver halide grains at a high sensitivity without giving rise to an adverse effect such as fog has been demanded.